1. Field of the Invention
This invention relates to an apparatus for the non-invasive detection and treatment of speech disorders, especially disorders effecting speech nasalization, and more particularly to such an apparatus for generation of quantitative predictive information related to underlying physiological and perceptual correlates of nasal resonance.
2. Description of the Prior Art
Early efforts at diagnosis and treatment of disorders of nasal resonance have been based on perceptual assessments of the patient's speech by the clinician. This approach has suffered for several reasons. Consistency of judgments among clinicians, dependent upon extensive clinical training, is often lacking. The subjective judgment is an assessment of the overall quality of the patient's speech, and therefore definition of specific attributes which give rise to the problem is poor. Feedback to the patient is delayed rather than immediate. Therefore, recent efforts have focused on development of methods which provide consistent, repeatable results with greater immediacy, and greater specificity with respect to definition of the problem.
In U.S. Pat. No. 3,752,929 to Fletcher is described a process and apparatus in which electrical signals representative of the sounds emitted from the nose and mouth are utilized to determine the degree of nasalance of speech. In this apparatus, a pair of sound-isolated microphones are carried in the housing adapted to be brought into place about the face of the patient in order to respectively measure sounds emanating from the nasal and oral cavities. The outputs of the microphones are filtered for respective frequency bands thought to have high nasal and oral content, and a ratio of the filtered microphone outputs computed to obtain a quotient signal which is then threshold detected against a reference representing a known degree of nasality. Then the output of the threshold detector is applied to a visual display such as a lamp by which the patient can determine whether or not a given sentence contains more or less nasalance relative to the reference established by the threshold detector.
The approach outlined in the Fletcher patent, which represented a major advance in providing a practical quantitative measure of disorders of nasal resonance, nevertheless requires that the patient place his face in the mask which provides acoustic isolation between the microphones and thereby permits separation of the oral and nasal acoustic signals. Unfortunately, the use of the facial mask requires that the patient place his head in a stable position, and further limits interaction between the patient and the clinician. This may present severe difficulties with young children or paralyzed patients who comprise a large percentage of the population seen in the clinic for defective velopharynseal valving. Furthermore, the degree of separation and acoustic isolation between the microphones has been questioned.
An alternate approach devised by Stephens et al, "A Miniature Accelerometer for Detecting Glottal Waveforms and Nasalization," J. Speech Hearing Res. 18 (1975), 594-599, utilized a light-weight accelerometer attached to the external surface of the nose for measuring nasal vibration during speech to obtain a quantitative measure related to nasality. Stephens et al filters, rectifies, and time averages the output of the accelerometer. Then, with the aid of a computer, the smooth signal is sampled, log converted and displayed on an oscilloscope to provide a visual display of nasalization.
In a related development, Garber et al, "The Effects of Feedback Filtering on Nasalization in Normal and Hypernasal Speakers," J. Speech Hearing Res. 22 (1979), 321-333, in order to investigate the effect of auditory feedback on vocal production and nasalization in particular, tested the effects on the nasalization of various subjects who listened to their speech filtered at various frequencies. Thus, Garber et al have investigated whether production of nasal quality would change when subjects hear their voices filtered. In implementing their study, Garber et al used the output of an accelerometer of the type employed by Stephens et al placed on the nose to obtain a measure of nasalization. The output of the accelerometer was first routed to a tape recorder. The recorded signal was later transferred to a graphic level recorder and analyzed through measurement of peaks in the signal with respect to a pre-recorded calibration tone. The arithmetic average of measured peaks constituted the nasalization score.
To validate the measurement, a preliminary study was conducted in which subjects were requested to speak at various intensity levels. The Pearson product-moment correlation between accelerometer output and perceptual judgments of nasality was 0.77. A correction factor was then introduced to compensate for intensity differences between the various conditions by subtracting each subject's vocal level from an arbitrary reference level, dividing this value by two, and adding it to the subject's nasalization score. After adjustment of scores in this manner, the correlation reported between accelerometer output and perceived nasality was 0.82. In this manner it was determined that the nasalization score accounted for 67% of the variance in nasality, provided that intensity level was held constant. An attempt was made to hold the intensity level constant in the main study described in the preceding paragraph by requesting subjects to speak at a constant vocal effort. A visual display of vocal intensity was provided to facilitate maintenance of constant vocal effort.
The measurement technique developed by Garber et al lacks instantaneous quantification and therefore lacks the immediate feedback necessary for efficient immediate modification of speech production. In the form implemented, the technique also requires that subjects maintain constant vocal effort to maximize accuracy of the measure.